The present invention relates to equipment utilized and operations performed in conjunction with a subterranean well and, more particularly, to systems and methods for protecting the lower main wellbore of whipstocks and completion deflectors from debris accumulation.
Hydrocarbons can be produced through relatively complex wellbores traversing a subterranean formation. Some wellbores can include multilateral wellbores and/or sidetrack wellbores. Multilateral wellbores include one or more lateral wellbores extending from a parent (or main) wellbore. A sidetrack wellbore is a wellbore that is diverted from a first general direction to a second general direction and can include a main wellbore in the first general direction and a secondary wellbore diverted from the main wellbore in the second general direction. A multilateral wellbore can include one or more windows or casing exits to allow corresponding lateral wellbores to be formed. A sidetrack wellbore can also include a window or casing exit to allow the wellbore to be diverted to the second general direction.
The casing exit for either multilateral or sidetrack wellbores can be formed by positioning a casing joint and a whipstock in a casing string at a desired location in the main wellbore. The whipstock is used to deflect one or more mills laterally (or in an alternative orientation) relative to the casing string. The deflected mill(s) penetrates part of the casing joint to form the casing exit in the casing string. Drill bits can be subsequently inserted through the casing exit in order to cut the lateral or secondary wellbore.
During lateral drilling operations, it is desirable to protect lower portions of the main wellbore from the accumulation of debris that results from drilling. Such debris can plug the main wellbore and prevent follow on operations such as retrieving whipstocks or deflectors or the opening of fluid loss devices. One way of preventing debris is through the use of mechanical barriers, such as flapper valves, plugs, disks, etc. With the accumulation of a large amount of debris, however, it may be difficult to subsequently open the flapper valve for follow on operations or retrieve the plug or disk from the main wellbore. Another way of preventing debris buildup in the main wellbore is by protecting the area in question with one or more viscous fluids. Formulating the appropriate viscosity or mixture of the viscous fluid for each wellbore application, however, can oftentimes be difficult and as a result large amounts of drilling debris will nonetheless continue to pass through the viscous fluid.